Nonmonotonic Coupled Dissolution-Precipitation Reactions at the Mineral–Water Interface |
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Authors: | Ashit Rao Subhash C Ayirala Mohammed B Alotaibi Michel H G Duits A A Yousef Frieder Mugele |
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Affiliation: | 1. Physics of Complex Fluids Group and MESA+ Institute, Faculty of Science and Technology, University of Twente, P.O. Box 217, Enschede, 7500 AE The Netherlands;2. The Exploration and Petroleum Engineering Center – Advanced Research Center (EXPEC ARC), Saudi Aramco, Dhahran, 34465 Saudi Arabia |
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Abstract: | Dissolution is inherent to fluid-mineral systems. Yet its impact on minerals reacting with electrolytes is overlooked. Here, a novel nonmonotonic behavior for the surface interactions of carbonates (calcite and Mg-calcite) with organic acids is reported. Applying a bioinspired approach, Mg-calcite sensors via amorphous precursors, avoiding any preconditioning with functional groups are synthesized. A quartz crystal microbalance is used to study the mass changes of the mineral on contact with organic acids under varying ionic conditions, temperatures, and flow velocities. Supported by confocal Raman microscopy and potentiometric titrations, nonmonotonous mass developments are found as a function of Ca2+ concentration and flowrate, and attributed to three coupled chemical reactions: i) carbonate dissolution via Ca2+ ion complexation with organic molecules, and the formation of organo-calcium compounds as ii) a surface phase at the mineral–water interface, and iii) particles in the bulk fluid. These processes depend on local ion contents and the precipitation onset (i.e., saturation index) of organo-calcium salts, both of which substantially differ in the bulk fluid and in the fluid boundary layer at mineral interfaces. This continuum between dissolution and precipitation provides a conceptual framework to address reactions at mineral interfacial across disciplines including biomineralization, ocean acidification and reservoir geochemistry. |
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Keywords: | adsorption calcium carbonate dissolution interfaces organic acids QCM-D |
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